Interaction of acetonitrile with olefins and alcohols in zeolite H-ZSM-5: In situ solid-state NMR characterization of the reaction products

The reaction products and intermediates from the interaction of acetonitrile with olefins (oct-1-ene) or alcohols (tert-butyl alcohol) in zeolite H-ZSM-5 at 296 K have been characterized with C-13 and N-15 solid-state NMR. It has been shown that coadsorption of acetonitrile and olefin on H-ZSM-5 gives rise to the intermediate N-alkylnitrilium cation, which is formed by trapping by the acetonitrile molecule of an unstable alkylcarbenium ion originating from the adsorbed olefin. The N-alkylnitrilium cation represents a persistent species inside a zeolite under anhydrous conditions. Upon admittance of water to the pores of the zeolite, the N-alkylnitrilium cation slowly converts into N-alkylamide in accordance with the classic Ritter reaction. In the case of acetonitrile and alcohol, just after coadsorption both the intermediate N-alkylnitrilium cation and the final N-alkylamide are identified simultaneously; the former slowly disappears over a few days. Thus, 1) it has been shown that the Ritter reaction can occur not only in liquid acidic media but also on a solid acid catalyst, zeolite H-ZSM-5; 2) N-alkylnitrilium cations have been detected and characterized with solid-state NMR as persistent intermediates in the Ritter reaction for the first time while the reaction proceeds.